Project Summary: Physical mechanical processes are central to the morphogenesis of embryos and their organs. The goal of this proposal is to apply a multi-scale analysis of the mechanics of convergent extension, identifying biomechanical mechanisms that establish passive tissue properties such as stiffness as well as active processes that generate forces of extension, regulate cell behaviors and tissue deformation, and how passive mechanics and active force generating processes are coordinated within the frog embryo. Studies outlined in this proposal will answer: (1) How are cell-scale structures and tissue mechanics are integrated during elongation? Early development is marked by dramatic changes in the mechanical properties of embryos. To understand how and why these properties change we test simple models of tissue mechanics based on synthetic closed-cell foams using bioengineering and biophysical methods to disrupt features from large scale architecture to the subcellular actomyosin-dependent cortex. (2) What single-cell mechanical processes contribute to convergent extension? We extend our analysis of cell behaviors to an unbiased approach that combines wide-field confocal microscopy with descriptive biomechanical analyses from the level of the cell, to the local neighborhood, to the strain fields of the entire embryo. Combining analyses of neural plate and paraxial somitic mesoderm we describe the dependence of these movements on planar polarity signaling. Using systems approaches we seek to test the dependencies of specific cell behaviors on both upstream signaling systems and their targeted downstream effectors. (3) How are tissue polarity cues transduced into polarized cell behaviors? We hypothesize that polarized cell behaviors and the oriented forces they generate are the result of cues produced by anisotropic strain. To test the roles of polarized intracellular factors and mechanical strain in organizing cell behaviors we use magnetogenetics and micro-scale tissue stretchers. Results from this project will complement ongoing efforts to identify the molecular regulators of morphogenesis by providing a conceptual framework developing new hypotheses of morphogenesis and bioengineering tools to test them. The significance of our work provides researchers a more complete understanding of the contribution of cell- and tissue-mechanics to development, to understand the role of tissue mechanics in oncogenesis, and to provide fundamental physical principles for future functional tissue engineers.